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Several new low-volatile pure monomer resins with varying softening points have been developed in response to general demand for low-VOC raw materials.
Pure monomer resins (PMRs) are produced from pure aromatic monomer streams, especially styrene and alkyl styrene derivatives. Major advantages of PMRs, compared to other aromatic crude C-9 resins, include light color (water white), excellent thermal stability, temperature resistance (similar to hydrogenated hydrocarbon resins) and controlled molecular weight.1-3
PMRs are typically manufactured using Lewis acids/ Friedel-Crafts catalysis of styrenic/alkyl styrenic monomer. Pennsylvania Industrial Chemical Corp./Hercules pioneered the process in early 1960s.4-7 Since then, several PMRs have been commercialized with varying vinyl aromatic chemistries and properties (softening points, molecular weight, etc.).
Using a proprietary processing technology, researchers recently developed several new PMRs that have very low residual monomer content and total volatile organic compound (VOC) content compared to traditional PMRs in the market. These new resins are based on a pure monomer resin product line that has been used for many years to modify styrenic block copolymers (SBCs), ethylene vinyl acetates (EVAs), and other polymers to balance cohesion, melt viscosity, and mechanical properties for various applications.8-15 This study is focused on evaluating the volatility characteristics of new low-volatile PMRs and their adhesive performance, especially in styrene isoprene styrene (SIS)-based pressure-sensitive adhesive (PSA) tape formulations.
RESULTS AND DISCUSSION
Resin properties of the low-volatile (LV) PMRs and traditional PMRs are given in Table 1. New LV PMRs show similar resin property characteristics as the traditional PMRs.
Residual monomer content and total VOC content of both traditional and new LV PMRs were analyzed using highperformance liquid chromatography (HPLC). HPLC has been employed by many in the industry to study the residual styrene content in several different applications.16 HPLC analysis was performed using Thermo-Fisher Hypersil gold column with an isocratic mobile phase. The peak area (UV wavelength monitored is at 200/210 nm), response factor (from 1-500 ppm), and sample weight were used to calculate the concentration of residual monomers and residual solvent...